Arrowhead Marsh - Oakland

looking towards downtown
CC SA-BY Our Oakland

Arrowhead Marsh is the main feature of the Martin Luther King Jr. Regional Shoreline. It's a popular area both with birds and birders. It's theorized that it was formed largely because of sediment washed down San Leandro Creek from the dam at Lake Chabot that Anthony Chabot was constructing in 1874. ¹

Birds

The marsh is one place to see the relatively rare Ridgway's rail. Numerous other species can be found there and nearby depending on the time of year, including Cooper's hawks, great blue herons, lesser egrets, pelicans, and of course various types of gulls.

Ridgway's rail CC SA-BY Our Oakland

Origin

excerpt of 1899 map ³

Chabot was constructing a dam as part of the East Bay water supply in 1874. In November of that year, heavy rains washed away part of the dam. When the dam was reconstructed, additional sediment was washed down. An article on OMCA's Guide to San Francisco Bay Area Creeks compares the area in coastal surveys in 1855 and 1895, and notes that by 1895 the arrowhead shape is starting to form. By a 1939 aerial photo, the shape is very similar to the present day form. ^1,2

Historic maps aren't much help in tracing the progress. Many of the older maps of Oakland don't extend that far, reflecting the historical bounds of the city. And most the maps were focused on the land features and roads, and depending on who they were made for, often showed proposed shorelines instead of what was actually there at the time. One of the earliest maps that Arrowhead appears on was a Shell street map from 1939, though there are later maps from other sources that don't show it.

Whether it was formed because of sediment from the dam or by some other source isn't clear. The evidence does suggest that it is relatively new, forming some time after 1855.